BMW DTC P21B1 – Reductant Level Sensor ‘C’ Circuit Intermittent/Erratic
DTC P21B1 meaning on BMW
The DTC P21B1 code for BMW indicates an intermittent or erratic signal from the Reductant Level Sensor ‘C’ circuit. This sensor is responsible for monitoring the level of the diesel exhaust fluid (DEF), also known as AdBlue, in the vehicle’s tank. The DEF is crucial for reducing harmful emissions in the exhaust system.
BMW DTC P21B1 symptoms
Symptoms of the DTC P21B1 code on a BMW may include:
- Check Engine Light (MIL) illuminated
- Reduced engine performance
- Possible DEF system warnings
BMW DTC P21B1 causes
Common causes of the DTC P21B1 code on a BMW include:
- Faulty Reductant Level Sensor ‘C’
- Wiring or connector issues in the sensor circuit
- Low DEF fluid level
- DEF contamination
BMW DTC P21B1 seriousness
The DTC P21B1 code should not be ignored as it can lead to increased emissions and potential compliance issues. Additionally, prolonged driving with this fault may cause damage to the vehicle’s emissions system.
How to diagnose DTC P21B1 on BMW
To diagnose the DTC P21B1 code on a BMW, you can follow these steps:
- Use a diagnostic scanner to retrieve the fault codes and freeze frame data
- Inspect the Reductant Level Sensor ‘C’ and its wiring for any visible damage
- Check the DEF fluid level and quality
- Perform a functional test of the sensor using a multimeter
How to fix DTC P21B1 on BMW
To fix the DTC P21B1 code on a BMW, you may need to:
- Replace the Reductant Level Sensor ‘C’ if it is found to be faulty
- Repair any damaged wiring or connectors in the sensor circuit
- Refill or replace the DEF fluid if the level is low or contaminated
- Clear the fault codes and perform a test drive to ensure the issue is resolved
How to erase DTC P21B1 on BMW
To erase the DTC P21B1 code on a BMW, you can use a diagnostic scanner to clear the fault codes from the vehicle’s memory. After clearing the codes, it is recommended to perform a test drive to verify that the issue has been resolved.
Recommended tools & DTC Scanners for BMW
Best Diagnostic App for modern BMWs: BimmerLink
Recommended Bluetooth adapter for Bimmerlink: OBDLink CX
Cable adapter for Bimmerlink: Enet Cable USB Type C
For older BMWs we recommend: Autel AutoLink AL319 (2024 version)
Easy-to-use Multimeter for reliable diagnostics: AstroAI Auto-ranging Multimeter
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